Cryptography Reference
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the target image into disjoint subimages), the priority mode (dividing the
target image according to the bitplanes), and the progressive mode (combining
the multisecret mode and the priority mode). To extend Wang and Shyu's
(2, n)-SSIS scheme, Yang and Huang proposed (t;n)-SSIS schemes where a
qualified set of participants consists of any t participants [13]. Two approaches
were proposed for a general construction for any t, 2 t n. For t = 2,
Approach 1 has the lesser shadow size than Wang and Shyu's (2, n)-SSIS
scheme, and Approach 2 is reduced to Wang and Shyu's (2, n)-SSIS scheme.
The following is the shadow constructing algorithm of their Approach 1.
Shadow Constructing Algorithm
Input: a secret image O.
Output: n shadows S
i
, i = 1, 2,, n.
n
t
n
t
Step 1. Divide image O into
subimages O
x
, x = 1. 2, ,
by
one of the three modes.
Step 2. For every image O
x
, use a polynomial-based (t;t)-SIS scheme to cre-
ate t subshadows (O
x
;O
x
; ;O
x
).
Step 3. Set S
1
= S
2
= = S
n
= .
Step 4. Choose a binary matrix B
n;t
= [b
i;j
].
n
t
Step 5. For j = 1 to
Set y = 1;
For i = 1 to n
If b
i;j
= 1 then O
j
=O
y
and y = y + 1.
else
O
j
=.
0
@
n
t
1
A
Step 6. S
1
=
S
O
j
, i=1,2,,n
j=1
n
t
The binary matrix B
n;t
= [b
i;j
] is a n
matrix, where b
i;j
2 [0; 1],
n
t
1 i n, and 1 i
. Every column vector has a Hamming weight
t. For example, the matrix B
n;t
=B
4;3
of a (3, 4)-SSIS scheme is
2
3
2
3
b
1;1
b
1;2
b
1;3
b
1;4
b
2;1
b
2;2
b
2;3
b
2;4
b
3;1
b
3;2
b
3;3
b
3;4
b
4;1
b
4;2
b
4;3
b
4;4
1
1
1
0
4
5
=
4
5
1
1
0
1
B
4;3
=
1
0
1
1
0
1
1
1
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